This study is designed to identify and compare the sensilla, associated with feeding on the tarsi and labella of both sexes of Tabanus nigrovittatus using scanning and transmission electron microscopy. To date sexual dimorphism with respect to mouthpart structure is evident and compliments function. In addition, behavioral and electrophysiological techniques will be used to determine the function of these sensilla. Chemosensilla have been located on the tarsi and labellum. A comparison will be made, using electrophysiological tecniques, of the peripheral chemosensory input of autogenous versus anautogenous females to various chemicals, including blood, to determine if failure of autogenous females to feed in the field is due to peripheral or central processing.